Antenna

ABSTRACT

An antenna system, particularly for vehicles. A discone-type antenna is preferably utilized for frequencies outside the vehicle. At various frequencies, either or both the antenna and the vehicle serve as exciters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 635,402, entitled “In-Vehicle Exciter”, toChadwick, filed on Nov. 27, 2000, and U.S. patent application Ser. No.10/160,747, entitled “Exciter System and Excitation Methods forCommunications Within and Very Near to Vehicles”, to Chadwick, et al.,filed on May 30, 2002, and the specifications thereof are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention (Technical Field)

The present invention relates to an antenna and exciter systems forvehicles, such as automobiles, trucks, trains, buses, boats andaircraft.

2. Description of Related Art

Note that the following discussion refers to a number of publications byauthor(s) and year of publication, and that due to recent publicationdates certain publications are not to be considered as prior artvis-a-vis the present invention. Discussion of such publications hereinis given for more complete background and is not to be construed as anadmission that such publications are prior art for patentabilitydetermination purposes.

The automobile manufacturing industry is undergoing an industry widerevolution to provide connectivity to automobiles. This field ofendeavor has been coined as “telematics” by the automotive industry.Connectivity is required for AM/FM radio, cellular, GPS, internet andsatellite linkage. The first phase of this revolution has already begun.All high-end model automobiles, such as those produced by Chrysler,Daimler-Benz and Cadillac, have already eliminated external antennas onthe top side of their vehicles. These antennas have been moved to thefront and rear windows of the automobile. Many automobiles will be soequipped in the next several years.

Now that automobile connectivity is required for emergency services, thesurvival of the antennas becomes a paramount issue. Unfortunately, oneof the first things to be destroyed is the windows along with theirantennas. In a severe accident, the automobile may often be upside downwith the under-chassis pointed skyward. The telematics systems must beable to function even in this case.

The problem of providing a solution for a survivable antennaconnectivity for vehicles has presented a major challenge to engineersand technicians in the automotive industry. The development of methodsand apparatus that would supply a survivable antenna for vehicles wouldconstitute a major technological advance, and would satisfy a long feltneed within the automobile industry.

Several patents disclose an under-vehicle antenna. These include U.S.Pat. No. 2,111,398, entitled “Antenna Device” to Kippenberg; U.S. Pat.No. 2,073,336, entitled “Radio Ground Exciter” to Cook; and U.S. Pat.No. 4,968,984, entitled “Antenna Unit for a Vehicle” to Katoh, et al.None of these patents disclose the use of a discone-type of exciter.

Prior art discones do not have a coaxial cable extending through thecone portion. U.S. patent application Ser. No. 10/160,747, entitled“Exciter System and Excitation Methods for Communications Within andVery Near to Vehicles,” and U.S. patent application Ser. No. 635,402,entitled “In-Vehicle Exciter”, which are incorporated herein byreference, disclose a modified discone exciter, which is used forcommunications within a vehicle. The present invention is directed to amodified discone exciter, with a coaxial cable disposed in the cone, forcommunications outside the vehicle.

BRIEF SUMMARY OF THE INVENTION

The present invention relates to discone-type of antenna. This antennacomprises a disc; a cone comprising an apex and a base comprising adiameter, the disc positioned at the apex of the cone; and a coaxialcable disposed in an interior of the cone from the apex through the coneand extending outwardly beyond the cone. The antenna further preferablycomprises an insulator disposed between the disc and the cone.Preferably, a coaxial cable is disposed through a center of the diameterof the cone.

The antenna may be disposed on an exterior of the vehicle, andpreferably disposed under the exterior of the vehicle. Alternatively,the antenna may be disposed in an interior of a vehicle, or in astructure. The antenna preferably operates at a frequency in the rangeof between approximately 500 KHz and between approximately 8 GHz.

The present invention is also directed to an exciter system for avehicle. This system comprises an antenna disposed on or in a vehicle.The exciter system radiates exterior to the vehicle. The exciter systemoperates in at least three modes. These three modes comprise thefollowing: (1) the antenna radiates at a higher frequency; (2) thevehicle radiates at a lower frequency; and (3) both the antenna and thevehicle radiate at a transition frequency between the lower frequencyand the higher frequency.

The antenna preferably comprises a discone antenna. This discone antennapreferably comprises the discone antenna discussed above.

When the antenna is disposed under a vehicle, it is preferably disposednear a centerline of the vehicle, and most preferably disposed betweenapproximately one and two feet of a front of a vehicle (e.g. the frontbumper).

The lower frequency is determined by the size of the vehicle. The higherfrequency is determined by the size of the discone. The cone angle ispreferably between approximately 45 degrees and approximately 90degrees. The cone height is preferably between approximately 0.4 inchesand approximately 4 inches. The cable is preferably betweenapproximately 0.08 inches and approximately 0.25 inches. The diskdiameter is preferably at least 0.18 wavelengths in diameter at itslower operating frequency.

The present invention also relates to a method of excitation for sendingand receiving various frequencies to and from a vehicle. This methodcomprises: disposing an antenna on or in a vehicle; exciting the antennaat higher frequencies that radiate outside of the vehicle; exciting thevehicle at lower frequencies that radiate outside the vehicle; andexciting both the antenna and the vehicle at transition frequencies thatradiate outside the vehicle. A discone antenna, as discussed above, ispreferably utilized.

The present invention provides methods and apparatuses for providing anantenna or exciter system for vehicles. In the preferred embodiment, theantenna is a modified discone exciter. In another embodiment of theinvention, the invention comprises an exciter mounted on the undersideof the vehicle which is separated from the vehicle frame by a dielectricseparator. A signal is elicited from the exciter, and may be fed to awide variety of radio or other frequency devices onboard the vehicle.

A primary object of the present invention is to provide an antenna thathas a low profile in a vehicle.

It is another object of the present invention to provide an antenna thatmay be mounted under a vehicle.

Yet another object of the present invention is to provide an antennathat modifies a traditional discone-type of exciter.

A primary advantage of the present invention is that a low-cost,low-profile, effective antenna is provided.

Another advantage of the present invention is that the vehicle may beused as a direct radiator for the antenna.

Other objects, advantages and novel features, and further scope ofapplicability of the present invention will be set forth in part in thedetailed description to follow, taken in conjunction with theaccompanying drawings, and in part will become apparent to those skilledin the art upon examination of the following, or may be learned bypractice of the invention. The objects and advantages of the inventionmay be realized and attained by means of the instrumentalities andcombinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The accompanying drawings, which are incorporated into and form a partof the specification, illustrate one or more embodiments of the presentinvention and, together with the description, serve to explain theprinciples of the invention. The drawings are only for the purpose ofillustrating one or more preferred embodiments of the invention and arenot to be construed as limiting the invention. In the drawings:

FIG. 1 is a side section view of the preferred embodiment of the presentinvention, showing a modified discone exciter;

FIG. 2 is a diagram of the evolution of the present invention;

FIG. 3A is a perspective cutaway view of an embodiment of the presentinvention intended for AM/FM radio applications;

FIG. 3B is a section view of the FIG. 3A embodiment;

FIG. 4 is a perspective cutaway view of another embodiment of thepresent invention;

FIG. 5 is a perspective cutaway view of a spiral embodiment of thepresent invention;

FIG. 6 is a graph of VSWR versus frequency for a PCS match;

FIGS. 7-11 show azimuth and elevation patterns at varying frequencies;

FIG. 12 is the measured return loss for various frequencies;

FIG. 13 is the measured VSWR for various frequencies;

FIGS. 14-20 show data comparison at various frequencies;

FIG. 21 shows a test range setup;

FIG. 22 shows patterns and absolute gain; and

FIGS. 23-25 show comparisons of the antenna location at variousfrequencies.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to antenna systems, particularly foruse on vehicles, such as automobiles, trucks, trains, buses, boats,aircraft, and the like. The antenna operates at particular frequencies,such that at high frequencies, the antenna radiates and at lowerfrequencies, there is a transition so that the vehicle, itself,radiates. The preferred type of antenna, useful in the presentinvention, is a discone-type of antenna.

The terms “antenna” and “exciter” are used interchangeably throughoutthe specification and claims and are intended to mean a system forsending and receiving electromagnetic waves and to generate or producean electric field. The term “discone” is intended to mean a particulartype of antenna or exciter, having disc and cone components, and thisterm is also intended to cover “disc-cone” or other such exciters havingthis configuration. Although the invention is discussed as to a singleantenna or exciter, multiple exciters may be utilized in or on a singlevehicle.

The antenna of the present invention is particularly useful forvehicles. In vehicles, there are three modes of operation: the antennaserving as the exciter; the vehicle serving as the exciter; and atransition between the antenna and vehicle, both as exciters. At higherfrequencies, when the size of the vehicle is large, the discone assemblyis the major component that radiates. At lower frequencies, the vehicleitself radiates. Both the vehicle and antenna radiate at transitionfrequencies. Frequencies over all these ranges vary from betweenapproximately 500 KHz to 8 GHz.

The frequencies in each of the ranges depend highly on the size of thevehicle. Three examples are given below, one for an automobile, one fora train and one for an airplane, using the following formula:Wavelength=11.8/frequency.Where f is in GHz, 11.8 is a constant for the speed of light, i.e. iff=1 GHz, then the above becomes 11.8″ wavelength.

Assume the car is 20 feet long. Its first resonance will occur wherethis dimension is ¼ (preferred) wavelength. Thus, the first resonantfrequency, using the above formula, is 12.3 MHz (11.8/240inches×1000×¼). This frequency sets the low end of the intermediate ortransition band. If the car also has a quarter wavelength monopoleoperating at 1 GHz, the upper end of the band is 1 GHz. And, thus, theintermediate band extends from approximately 12.3 MHz to 1 GHz.

If there is a metal railroad car which is 50 feet long, then the firstresonant frequency, using the above formula, is 4.9 MHz. Theintermediate band is thus 4.9 MHz to 1 GHz.

For an airplane, 100 feet long, the first resonant frequency, using theabove formula, is 2.46 MHz. The upper end is 1 GHz.

As can be seen by the above, the frequency ranges are highly dependenton the length of the vehicle. Structure and antenna size also affect thefrequencies.

The upper range of frequencies is generally set at less than or equal to⅛ wavelength, although a range of between approximately 1/16 and ¼wavelength is useful in accordance with the present invention. The sizeof the discone or antenna also determines this range. For a discone, itis useful to have the top plate at approximately 0.7 diameter of thebase diameter.

The lower range is set by the size of the vehicle.

The intermediate or transition range is between the upper and lowerranges.

The antenna principally serves as a transition from itself to thevehicle and the antenna then acts as a direct radiator working againstthe vehicle skin (as with a ground plane). The antenna preferably has abandwidth of approximately 100 to 1 or up to approximately 200 to 1.

The antenna is preferably mounted outside the vehicle, and mostpreferably on the underside of the vehicle in order to minimize damagein the event of a crash. However, the antenna may be mounted at anyplace inside or outside the vehicle, preferably at a location thatavoids interference with other functions of the vehicle or preventsinterference with the antenna. For instance, it could be positioned onthe back or front window ledges, near the bumper, etc. The antenna iscapable of sending and receiving frequencies to and from outside thevehicle due to the particular frequencies.

The transition frequency from one mode to the other is a vehicle sizeand configuration variable. The lowest limit occurs where the size ofthe vehicle is approximately a quarter wavelength long and the match isgood. Below the lower limit the match gradually degrades to a poorer andpoorer value because the automobile is becoming smaller than thewavelengths. Above the lower limit region the loss is approximately 50%until the mode of operation where the antenna begins to act as a nearindependent radiator. The independent mode can be very match efficient.

In the low frequency region the match is poorest but the longwavelengths have less propagation loss and thus the match loss isgenerally acceptable. In the region above 60 MHz the 50% match loss canbe reduced over limited bands by the use of diplexers and matchingelements. In the upper region, the match is quite good (preferably from800 MHz to 2 GHz).

The frequency zones are defined but radiation characteristics must bequantified. For frequencies about 60 MHz the radiation shape is that ofa cardiod, being near omnidirectional in azimuth and similar to that ofa monopole over a ground plane in elevation. As the frequency increases,the pattern is overall the same but with more fine structural detail asthe frequency approaches 800 MHz. In the region from 800 MHz to 8.0 GHzthe patterns are much like the low end except for automobile inducedblockage effects.

The characteristics of the antenna, when applied to larger trucks andvans differ in details from those above described for an automobile. Thecharacteristics referred to are those of match, patterns and gain. Theperformance from 800 MHz to 2.0 GHz (preferred range) is the same as inan automobile except for blockage detail. The intermediate range is nowdependent on the size of the truck or van, but will generally be lowerin frequency. The first resonance will generally be below 60 MHz becausethe truck is larger.

FIG. 1 is a depiction of the preferred discone antenna of the presentinvention. As shown therein, discone antenna comprises cone 10(preferably a solid cone), disc 12, coaxial cable 14 which extendsthrough cone to disc, cable connector 16, ground plane (e.g.undercarriage of automobile) 18, and preferably insulating spacer 20.

Coaxial cable 14 is connected to devices in the vehicle that receive ortransmit various frequencies to or from outside the vehicle. Theseinclude AM/FM radio, GPS, cellular, internet, satellite linkage, garagedoor, gate and other outside devices, traffic control, roadside antenna,vehicle identification, video transfer, light and other electronicscontrol, and the like. Wireless connections may also be utilized inaccordance with the present invention.

The antenna of the present invention incorporates the vehicle (at lowfrequencies). This antenna is preferably located within one to two feetof the front bumper of the vehicle (e.g. automobile or truck) and nearthe centerline of the vehicle. The dimensions are selected to keep thematch and pattern shapes acceptable. Cone angle 22 is preferablyapproximately 60 degrees but can vary between approximate 45 degrees andapproximately 90 degrees. Cone height is preferably betweenapproximately 0.5 inches and approximately 12 inches, preferably betweenapproximately one and approximately four inches and most preferablybetween approximately two and approximately three inches (e.g. 2.84inches). Coaxial cable 14 diameter is preferably between approximately0.1 inches and approximately 0.2 inches (e.g. 0.141 inch diameter). Disc13 diameter is at least 0.18 (e.g. 0.18 to 0.5 wavelengths) wavelengthsin diameter at the lowest operating frequency (see FIG. 1).

When the discone is attached to the undersurface of the vehicle, disc 12is positioned at the lowest level of cone 10. Ground plane 18 isintended to attach to the underside of the vehicle after validation isfirst obtained on the free space range.

INDUSTRIAL APPLICABILITY

The invention is further illustrated by the following non-limitingexamples.

EXAMPLE 1

Initial data was first taken on a free space range and included theground plane shown in FIG. 1. The match of the antenna is shown in FIG.6. The VSWR is less than 2:1 from 600 MHz to 1800 MHz. The VSWR is lessthan 3:1 from 580 MHz to 2 GHz. The azimuth and elevation patterns areshown in FIGS. 7 through 11. The azimuth patterns are omnidirectionalwith 1 dB from 800 MHZ to 1.5 GHz and less than 2 dB to 1.9 GHz. Theelevation patterns are typical cardiods over the entire band. The 0degree reference was at the base of the ground plane. The results wereconsidered adequate and the next phase was the testing of an automobilemounted antenna.

EXAMPLE 2

The FIG. 1 antenna was positioned 9″ from the centerline of the frontbumper of an automobile. The measured return loss is shown in FIG. 14and measured VSWR is shown in FIG. 13. The VSWR is less than 3 to 1 fromapproximately 620 MHz to 2 GHz. The effect of VSWR on the vehicle isquite small as shown in the comparison of FIG. 6.

Measured patterns are shown in FIGS. 14 through 16 for frequencies of850 MHz, 1575 MHz and 1850 MHz and at elevation heights of 1, 3 and 5feet (the transmitter was located approximately 10 feet away from thevehicle). The 850 MHz frequency generally provided the same response,however, the front lobe was typically 20 dB stronger than the rear lobe.The 1575 MHz frequency provided better coverage for heights of 1-3 feetabove the ground and 10 feet away, but was reduced at an elevation of 5feet. At 1575 MHz the front lobe was typically 20 dB stronger than therear lobe. At 1850 MHz the front lobe was typically 20 dB stronger thanthe rear lobe and the pattern levels reduced slightly above 3 feet. Thegain values are shown in FIG. 17 for all three frequencies. The absolutegains are measured in the forward 0 degree direction and are 5.4, 4.5,and −3.3 dBi. The gains were typically greater than a dipole in theforward direction, largely because the back lobe in all cases wasapproximately 20 dB lower. The gain data were obtained by thesubstitution method.

EXAMPLE 3

The relative gains of an analog cell phone stub antenna, GPS stubantenna and PCS stub antenna are shown in FIGS. 18 through 20 comparedwith the antenna of the present invention. The antenna of the presentinvention was stronger over most of the region except for the rearwarddirection. The stub antennas for each unit were located on the consolebetween the driver and passenger seats. The stub antennas were mountedvertically to match the testing antenna polarization. The test rangelayout is shown in FIG. 21.

EXAMPLE 4

GPS test data were taken on the stub antenna of the present inventionduring actual driving conditions from Santa Clara to Lodi Calif., a 215mile round trip. The average accuracy was 22 feet and compared well withthe stub which provided accuracy from 20 to 26 feet at DRG. On averagethere were 6 to 10 satellites in view during the trip taken. The 22 footaccuracy was maintained through the foothill passes. The unit hadreadings as low as 16 feet and as high as 50 feet. The average durationof greater than 30 feet was 2 seconds. The most common accuracy was 18feet. The satellites with the stronger signal strength were generallylocated overhead and forward, while those located to the rear and lowhorizon had the lower signal strength.

Both an analog and PCS phone were used to make connections. The measuredsignal strength on the phone indicators for both the antenna and themanufacturers' stub antennas were the same. The quality of the phonereceptions appeared to be approximately the same.

The antenna of FIG. 1 was moved to the center of the automobile and waslocated under the passenger near center of the vehicle. FIG. 22 showsthe patterns and the absolute gain at the three frequencies of 850, 1575and 1850 MHz. The patterns are more symmetric than those located at thefront of the vehicle. At 1850 MHz there was a significant notch at 30degrees. FIGS. 23 through 25 show direction comparisons with the datataken when the antenna was at the front of the vehicle. The centermounted data was generally more uniform as expected. The relative gainof the center mounted antenna showed the increased interference of thevehicle undersurface.

EXAMPLE 5

The same structure used in FIG. 1 also served as an antenna for anintermediate range (50 to 800 MHz) in an automobile. In this casehowever, the major radiator transitioned from a body radiating device to50 MHz to a partial body device as the frequency approached 800 MHz. Theantenna design was the same except that the disk was approximately 6inches in diameter for case 1. A 12 inch diameter disc produced farbetter results. The lower frequency resonance occurred in the regionjust below 60 MHz and had a mismatch that was generally less than 2:1over a narrow bandwidth.

EXAMPLE 6

The VSWR and loss data when the antenna was mounted on an automobile isshown in FIG. 22. The reference point is the antenna terminal. The VSWRinflection point occurred at approximately 325 MHz for a 6 inch disk andat approximately 125 MHz for the 12 inch disk. The correspondinginflections for loss are shown in FIG. 22 for both the 6 and 12 inchdisk. The improvement from 6 to 12 inches was dramatic. A 12 inch diskat 115 MHz had a 3 dB loss and at 230 MHz it had a 1 dB loss. A 6 inchdisk had a 3 dB loss at 260 MHz and a 1 dB loss at 314 MHz. Theapproximate rule for selecting the disk diameter for a loss of 3 dB is0.18 times the wavelength of the lowest operating frequency. Themeasured patterns in the azimuth plane at 1 foot elevation are shown inFIG. 23 for frequencies of 98 and 325 MHz. The pattern levels shown wererelative. The patterns were taken with a disk diameter of 12 inches. Thepeak gain at 98 MHz was −4.8 dBi including match losses (4.3 dB) in theantenna. The peak gain at 325 MhZ was −6.0 dBi including match losses(1.5 dB) in the antenna. No pattern data was taken on the 6 inch disk.Absolute gains were obtained with a gain standard. The application ofsimple matching using a transformer and an inductor provided a maximumloss of 1.4 dB over the region from 86 MHz to 110 MHz using a 12 inchdisk. This matching increased the gain from the earlier noted −4.8 dBito −1.8 dBi. A 12 inch disk was used to receive FM signals over the fullFM band. The results were compared with a standard automobile whipantenna. There was no discernable difference between the antenna with a12 inch disk and the whip antenna.

Although the invention has been described in detail with particularreference to these preferred embodiments, other embodiments can achievethe same results. Variations and modifications of the present inventionwill be obvious to those skilled in the art and it is intended to coverin the appended claims all such modifications and equivalents. Theentire disclosures of all references, applications, patents, andpublications cited above are hereby incorporated by reference.

1. A discone-type of antenna comprising: a disc; a cone comprising anapex and a base comprising a diameter, said disc positioned at said apexof said cone; and a coaxial cable disposed in an interior of said conefrom said apex through said cone and extending outwardly beyond saidcone.
 2. The antenna of claim 2 further comprising an insulator disposedbetween said disc and said cone.
 3. The antenna of claim 1 disposed onan exterior of a vehicle.
 4. The antenna of claim 3 disposed under saidexterior of the vehicle.
 5. The antenna of claim 1 disposed in aninterior of a vehicle.
 6. The antenna of claim 1 disposed in astructure.
 7. The antenna of claim 1 having a frequency in the range ofbetween approximately 500 KHz and between approximately 8 GHz.
 8. Theantenna of claim 1, wherein said coaxial cable is disposed through acenter of said diameter of said cone. 9-29. (canceled)
 30. In a vehiclehaving transmitting and/or receiving communication equipment and a bodythat is in part metallic, an exciter system having broad bandwidthsend/receive capability including an antenna mounted on or in thevehicle radiating at high and intermediate frequencies and acting as adirect radiator on the vehicle body causing the body to radiate at lowerand intermediate frequencies.
 31. The exciter system of claim 30 whereinthe lower frequency radiation limit is the vehicle body size defined bythe one-quarter wavelength of the radiation.
 32. The exciter system ofclaim 30 wherein the intermediate frequencies comprise a transitionfrequency range.
 33. The exciter system of claim 32 wherein thetransition frequency is defined by the vehicle size and configuration.34. The exciter system of claim 30 wherein the high frequency range isbetween 800 MHz and 2 GHz.
 35. The exciter system of claim 31 whereinthe low frequency radiation limit is 60 MHz.
 36. The exciter system ofclaim 35 wherein the low frequency radiation shape is a cadioid.
 37. Theexciter system of claim 36 wherein the low frequency radiation shape isomnidirectional in azimuth.
 38. An exciter system comprising a disconeantenna and an automobile metallic body acting as an antenna, the twoantenna radiating over the frequency range of 600 KHz to 2 GHz.
 39. Theexciter system of claim 38 wherein said discone antenna is mountedbeneath the automobile body.
 40. The exciter system of claim 38 whereinthe discone cone height is between 0.5 and 12 inches.
 41. The excitersystem of claim 40 wherein the disc diameter is between 0.18 and 0.5wavelengths.